1. Cross-Reference to Related Cases
Some of the dyes included in the claims of the present case are included in examples of eutectic combinations of dyes for thermal imaging in 3M Pat. application No. SN 193,947 filed on May 13, 1988.
2. Field of Invention
This invention relates to thermal imaging and, more particularly, to anthraquinone dyes bearing sulfonylamino substituents which are useful for thermal dye transfer imaging.
3. Background of the Art
The term thermal printing covers two main technology areas. In thermal transfer printing of textiles, a donor sheet is coated with a pattern of one or more dyes, contacted with the fabric to be printed, and heat is uniformly administered, sometimes with concomitant application of a vacuum. The transfer process has been much studied, and it is generally accepted that the dyes are transferred by sublimation in the vapor phase. Pertinent references include: C. J. Bent et al., J. Soc. Dyers Colour., 85, 606 (1969); J. Griffiths and F. Jones, ibid., 93, 176, (1977); J. Aihara et al., Am. Dyest. Rep., 64, 46 (1975); C. E. Vellins in "The Chemistry of Synthetic Dyes", K. Venkataraman, ed., Vol. VIII, 191, Academic Press, New York, 1978.
The other area covered by the term thermal printing is thermal imaging, where heat is applied in an imagewise fashion to a donor sheet in contact with a suitable receptor sheet to form a colored image on the receptor. In one embodiment of thermal imaging, termed thermal mass transfer printing, as described for instance in U.S. Pat. No. 3,898,086, the donor is a colorant dispersed in a wax-containing coating. On the application of heat, the construction melts or is softened and a portion of the colored donor coating transfers to the receptor. Despite problems with transparency, pigments are generally the colorants of choice in order to provide sufficient light fastness of the colored image on the receptor. Another embodiment is termed variously thermal dye transfer imaging or recording, or dye diffusion thermal transfer. In this embodiment, the donor sheet comprises a dye in a binder. On imagewise application of heat, the dye, but not the binder, is transferred to the receptor sheet. A recent review has described the transfer mechanism as a "melt state" diffusion process quite distinct from the sublimation attending textile printing. (See: P. Gregory, Chem. Brit., 25, 47 (1989)).
This same review emphasizes the great difficulty of developing dyes suitable for diffusive thermal transfer, stating that "It is significant that of the one million or so dyes available in the world, none were fully satisfactory". Among the failings of said dyes are inadequate light and heat fastness of the image and insufficient solubility of dyes for coating in the donor sheet. As has been noted previously, light fastness is also a problem in mass transfer imaging systems. In fact, achieving adequate light fastness is probably the single biggest challenge in these constructions. In large measure this is the result of the diffusive thermal transfer dye image being a surface coating a few microns thick. The dye is thus readily susceptible to photooxidative degradation. In contrast, textile fibers, which are 100 times thicker, are uniformly dyed throughout their depth, so that fading in the first few microns at the surface is of little practical importance. In consequence, it is common to find that dyes showing good light fastness in textile printing exhibit very poor photostablity in diffusive thermal transfer imaging (see e.g., U.S. Pat. No. 4,808,568), and there remains a strong need for improved dyes for the latter application.
Although thermal printing of textiles bears a superficial resemblance to diffusive thermal dye imaging, in reality quite different processes with distinct properties and material requirements are involved. Thermal printing occurs by a sublimation process, so that substantial vapor pressure is a prime criterion for dye selection. In diffusive dye imaging, high vapor pressure of the dye contributes to undesirable thermal fugacity of the image. For the melt state diffusion process involved in this situation, melting point is instead a better basis for dye selection. Diffusive dye transfer is a high resolution dry imaging process in which dye from a uniform donor sheet is transferred in an imagewise fashion by differential heating to a very smooth receptor, using heated areas typically of 0.0001 square inches or less. In contrast, the thermal printing of textiles is of comparatively low resolution, involving contemporaneous transfer by uniform heating of dye from a patterned, shaped or masked donor sheet over areas of tens of square feet. The typical receptors printed in this manner are woven nor knitted fabrics and carpets. The distinct transfer mechanism allows such rough substrates to be used, while diffusive imaging, where receptors with a mean surface roughness of less than 10 microns are used, is unsuitable for these materials. Unlike diffusive thermal dye imaging, the transfer printing process is not always a dry process; some fabrics or dyes require pre-swelling of the receptor with a solvent or a steam post-treatment for dye fixation. Though the transfer temperatures for the two processes can be similar (180.degree. to 220.degree. C.), diffusive dye transfer generally operates at somewhat higher temperatures. However, in a manner strikingly reflective of the differences in mechanism involved, diffusive dye transfer involves times of around 5 msec, whereas thermal printing normally requires times of 15 to 60 sec. In accord with the sublimation process involved, thermal printing often benefits from reduced atmospheric pressure or from flow of heated gas through the donor sheet. Thermal printing is a technology developed for coloring of textiles and is used to apply uniformly colored areas of a predetermined pattern to rough substrates. In contradistinction, diffusive dye transfer is a technology intended for high quality imaging, typically from electronic sources. Here, a broad color gamut is built with multiple images from donors of the three primary colors onto a smooth receptor. The different transfer mechanism allows the requirement for grey scale capability to be fulfilled, since the amount of dye transferred is proportional to the heat energy applied. In thermal printing grey scale capability is expressly shunned, because sensitivity of transfer to temperature decreases process latitude and dyeing reproducibility.
It now has been found that anthraquinone dyes bearing alkyl- or arylsulfonylamino groups can be beneficially used in thermal dye transfer imaging. When these dyes are used in dye donor constructions, the resultant transferred images exhibit improved light and heat fastness over comparable materials known in the art. Surprisingly, many of these dyes are conventional materials well known in the art. Others, however, are novel and are described in copending application Ser. No. 07/384,157 filed the same day as this application. The latter additionally offer improved solubility in the hydrocarbon solvents required for dye donor sheet coating.
Very little mention is made of sulfonylaminoanthraquinone dyes in the thermal printing art. European Pat. No. 20292 Al describes an auxiliary support for the thermal printing of textiles, characterized by porosity or perforations permitting a specified air flow, and coated with a pattern of dyes to be transferred to the fabric. The dyes are specified as those which volatilize without significant decomposition below 310.degree. C., and whose volatility is less than that of the least volatile of the colorants used for classical printing by transfer in the gas phase. Among other dyes, 1-(4'-tolylsulfonylamino)-4-hydroxyanthraquinone is described as suited to this application. In Example 3 of this disclosure, this dye is described as giving a violet ink. Since this dye is in fact orange, it is likely a misidentification has been made. A plausible alternative structure would be 1-(4'-tolylamino)-4-hydroxyanthraquinone, which is mentioned in claim 10 of said patent. Auxiliary supports are again described in U.S. Pat. No. 4,369,038, which are useful for thermal printing of cotton fibres swollen with polyethylene glycol. The dyes to be used on said sheet are characterized as giving poor density of dyeing when applied under the conventional conditions of 35 seconds at 205.degree. C., but giving dyeings of densities comparable to those of dyes used effectively under conventional conditions only when applied at 235.degree. C. under a reduced pressure of 50 to 120 mbars (i.e about 0.05 to 0.12 atm). It is further required that the dyes change to the vapor state below 320.degree. C. at atmospheric pressure. 1-amino-2-methoxy-4-(4'-tolylsulfonylamino)anthraquinone is mentioned as a dye which can be used for this purpose. The same dye is disclosed in U.S. Pat. No. 4,682,983, which claims a transfer sheet for heat transfer printing of textile materials which contain cellulosic fibers pretreated for swelling, said sheet comprising a flexible substrate coated with a release layer to which is applied a dyestuff coating or design. The dyestuff coating is characterized as a mixture of a binder and at least one disperse or vat dyestuff. This dyestuff has further additional characteristics: it does not "sublimate" in conventional heat transfer printing; it has an optical density not exceeding 0.3 as a saturated solution in boiling 0.1 molar aqueous sodium carbonate; it is transferred at no more than 40% by weight under conventional transfer conditions (200.degree. C., 30 seconds, normal atmospheric pressure) and with relatively low contact pressure (5 kPa); it is transferred more than 60% by weight under high contact pressure (50 kPa) at 230.degree. C. for 30 seconds at a reduced atmospheric pressure of 10,000 Pa (about 0.1 atm).
Japanese Kokai JP48-01387 describes a method of heat-transfer printing of cellulose with reactive sublimation dyes, in which the cellulose is pretreated with acid absorber and reaction accelerator. Among a range of reactive dyes disclosed are anthraquinone dyes bearing a 1-NHX group and a 4-hydroxy or 4-amino group and also anthraquinone dyes having a 1-NMeX-2-cyano-4hydroxy substitution pattern. The group X includes --SO.sub.2 CH.sub.2 CH.sub.2 Cl and --SO.sub.2 CH.dbd.CH.sub.2. The explicit example of 1-vinylsulfonylamino-4-aminoanthraquinone is provided, which is described as a blue dye, but is more likely magenta.
The thermal printing art for textiles discloses only 1-vinylsulfonylamino- and 1-(2'-chloroethylsulfonylamino)anthraquinones bearing additional auxochromic substituents, along with 1-amino-2-methoxy-4-(4'-tolylsulfonylamino)anthraquinone. These are characterized as sublimation dyes, and are uniformly transferred to substrates which require special pretreatment. The conditions of use are far removed from those which obtain for the different process of diffusive thermal dye imaging. There is, thus, no thermal printing art which is directly pertinent to the present invention.
Many sulfonylaminoanthraquinone dyes are well-known in the dyeing art. Thus, 1-amino-2-OR-4-alkylsulfonylaminoanthraquinones (R being alkyl or aryl) are described in U.S. Pat. Nos. 3,072,683, 3,391,164, 3,763,192, 3,894,060, and in British Pat. No. 1,015,505 and British Pat. No. 1,478,022. Similar 1-amino-2-thioalkyl-4-alkylsulfonylaminoanthraquinones are disclosed in U.S. Pat. Nos. 2,640,059, 3,394,133, 3,642,425 and U.S. Pat. No.3,822,992. Also known are the 1-amino-2-sulfo-4-alkylsulfonylaminoanthraquinones (see U.S. Pat. No. 1,928,725 and British Pat. No. 790,952), but these are less desirable in thermal dye transfer imaging because of the presence of the ionizable sulfo group limits compatibility with the hydrocarbon-based binders and solvents used in the dye donor sheets. Other alkylsulfonylaminoanthraquinone derivatives can be found in U.S. Pat. No. 3,532,723 and U.S. Pat. No. 3,350,425. Anthraquinones with more than one alkylsulfonylamino substituent are mentioned in U.S. Pat. No. 3,209,016 and in the abstract of Japanese Kokai No. 63-258955. Among the arylsulfonylaminoanthraquinones a wide variety of 1-amino-2-OR-4-arylsulfonylaminoanthraquinones are known. These are disclosed, for example, in U.S. Pat. Nos. 1,948,183, 3,087,773, 3,428,411, 3,467,681, 3,507,606, and U.S. Pat. No. 4,110,072. Other arylsulfonylamino-derivatives are described in U.S. Pat. Nos. 1,939,218, 3,240,551, 3,486,837 and U.S. Pat. No. 3,734,933, in German Pat. No. 623,069 and German Pat. No. 647,406, in U.S. Defensive Publication No. T873,014, and in R. H. Hall and D. H. Hey, J. Chem. Soc., 736 (1948).